1. Field of the Invention
The present invention relates to a discharge lamp lighting apparatus for lighting a discharge lamp used for, for example, a liquid crystal display unit.
2. Description of the Related Art
There is a discharge lamp lighting apparatus that employs a burst dimming pulse signal to control the brightness of a discharge lamp to a desired level. This apparatus starts and stops an ON/OFF operation of switching elements such as p-type and n-type FETs according to the burst dimming pulse signal, thereby controlling the brightness of the discharge lamp.
There is a discharge lamp lighting apparatus of this type that conducts a soft start operation during a burst dimming operation. An example of this type of discharge lamp lighting apparatus is described in Japanese Unexamined Patent Application Publication No. 2004-166446. The apparatus of this related art employs a transformer having a primary winding connected to a semiconductor switch circuit and a secondary winding connected to a load. The related art carries out PWM control on each switch in the semiconductor switch circuit, to realize an inverter that passes a constant current to the load. The related art also controls an intermittent operation during the burst dimming operation.
Namely, in each OFF interval in the burst dimming operation, the related art zeroes an error signal used for the PWM control. In addition, at the start and end of an ON or OFF interval of the burst dimming operation, the related art gradually increases or decreases the error signal used for the PWM control by charging and discharging a capacitor of a feedback circuit, to slowly start or end the PWM control, which works to provide a constant current.